Microtomes are used to prepare very thin specimens, and usually include a knife holder for holding a replaceable knife, and a specimen holder for holding a sample, the sample being moved toward the knife by a feeding mechanism. Ultramicrotomes are used to produce extremely thin sections, such as are used, for example, for transmission electron microscopy. The section thickness is typically in the range from 10 to 500 nm.
Examples of applications include material analysis or examination of soft materials from medical and biological sources. To render the soft materials cuttable, they are embedded in a liquid hardening substance, such as gelatin or synthetic resins.
The replaceable knives used are steel or hard metal knives of different profiles. In ultramicrotomes, glass and diamond knives are used.
The sharpness and hardness of the knives are decisive for a good result and the quality of the sections. Depending on whether hard or soft samples are cut, the knives wear to different degrees. For example, to produce ultrathin sections in an ultramicrotome, expensive diamond knives having cutting edge widths of up to 8 mm are used, the width of wear being within the range of the width of the sample to be sectioned, which is approximately 0.25 mm. When working with a very hard sample, the knife may already be so worn after fewer than ten cuts that proper use is no longer possible.
Therefore, care must be taken to use different portions of the knife edge and to ensure uniform wear of the cutting edge. However, the quality of the knife edge, i.e., the wear thereof, cannot be determined by observation using a stereomicroscope, for example.
Therefore, when using the knives, the user selects a portion for cutting in a more or less arbitrary manner, or switches between such portions during cutting according to his or her subjective assessment. In order not to jeopardize the quality of the sections, knives are frequently replaced with new ones as a precaution. At present, therefore, knives are replaced more or less on speculation, especially if the microtome has not been used for an extended period of time, or if it is used by different users who do not have any information about the wear condition of the knife edge.
This leads to unnecessary costs since knives are replaced or resharpened before the end of their useful lives.